| 1. |
- Dahlström, J. Marcus, 1982-, et al.
(author)
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Theory of attosecond delays in laser-assisted photoionization
- 2013
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In: Chemical Physics. - : Elsevier BV. - 0301-0104 .- 1873-4421. ; 414, s. 53-64
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Journal article (peer-reviewed)abstract
- We study the temporal aspects of laser-assisted extreme ultraviolet (XUV) photoionization using attosecond pulses of harmonic radiation. The aim of this paper is to establish the general form of the phase of the relevant transition amplitudes and to make the connection with the time-delays that have been recently measured in experiments. We find that the overall phase contains two distinct types of contributions: one is expressed in terms of the phase-shifts of the photoelectron continuum wavefunction while the other is linked to continuum–continuum transitions induced by the infrared (IR) laser probe. Our formalism applies to both kinds of measurements reported so far, namely the ones using attosecond pulse trains of XUV harmonics and the others based on the use of isolated attosecond pulses (streaking). The connection between the phases and the time-delays is established with the help of finite difference approximations to the energy derivatives of the phases. The observed time-delay is a sum of two components: a one-photon Wigner-like delay and an universal delay that originates from the probing process itself.
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| 2. |
- Dahlström, Marcus, et al.
(author)
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Atomic and macroscopic measurements of attosecond pulse trains
- 2009
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In: Physical Review A (Atomic, Molecular and Optical Physics). - 1050-2947. ; 80:3
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Journal article (peer-reviewed)abstract
- We characterize attosecond pulses in a train using both the well established "reconstruction of attosecond beating by interference of two-photon transitions" (RABITT) technique and the recently demonstrated in situ method, which is based on a weak perturbation of the harmonic generation process by the second harmonic of the laser field. The latter technique determines the characteristics of the single atom emission, while RABITT allows one to measure attosecond pulses "on target." By comparing the results of the two methods, the influence of propagation and filtering on the attosecond pulses can be extracted.
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| 3. |
- Gisselbrecht, Mathieu, et al.
(author)
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Exploring single-photon ionization on the attosecond time scale
- 2012
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In: XXVII International Conference on Photonic, Electronic and Atomic Collisions (Icpeac 2011), Pts 1-15. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 388, s. 032025-032025
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Conference paper (peer-reviewed)abstract
- One of the fundamental processes in nature is the photoelectric effect in which an electron is ripped away from its atom via the interaction with a photon. This process was long believed to be instantaneous but with the development of attosecond pulses (1 as 10(-18) s) we can finally get an insight into its dynamic. Here we measure a delay in ionization time between two differently bound electrons. The outgoing electrons are created via ionization with a train of attosecond pulses and we probe their relative delay with a synchronized infrared laser. We demonstrate how this probe field influences the measured delays and show that this contribution can be estimated with a universal formula, which allows us to extract field free atomic data..
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| 4. |
- Guenot, Diego, et al.
(author)
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Photoemission time delay measurements and calculations close to the 3s ionization cross section minimum in ar
- 2012
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In: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 85:5, s. 053424-
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Journal article (peer-reviewed)abstract
- We present experimental measurements and theoretical calculations of photoionization time delays from the 3s and 3p shells in Ar in the photon energy range of 32-42 eV. The experimental measurements are performed by interferometry using attosecond pulse trains and the infrared laser used for their generation. The theoretical approach includes intershell correlation effects between the 3s and 3p shells within the framework of the random-phase approximation with exchange. The connection between single-photon ionization and the two-color two-photon ionization process used in the measurement is established using the recently developed asymptotic approximation for the complex transition amplitudes of laser-assisted photoionization. We compare and discuss the theoretical and experimental results, especially in the region where strong intershell correlations in the 3s -> kp channel lead to an induced Cooper minimum in the 3s ionization cross section.
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| 5. |
- Klünder, Kathrin
(author)
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Electron Wave Packet Dynamics on the Attosecond Time Scale
- 2012
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Doctoral thesis (other academic/artistic)abstract
- One objective of attosecond science is to study electron dynamics in atoms and molecular systems on their natural time scale. This can be done using attosecond light pulses. Attosecond pulses are produced in a process called high-order harmonic generation, in which a short, intense laser pulse interacts with atoms or molecules in a highly nonlinear process, leading to the generation of high-order frequencies of the fundamental laser with a large spectral bandwidth, supporting pulses with attosecond duration. In some condition the harmonics are locked in phase leading to a train of attosecond pulses or, in some cases, to a single attosecond pulse. This thesis presents experiments based on interferometry to study electron dynamics using attosecond pulses. The first part describes a series of experiments, in which the dynamics of electrons was studied after photoionization with an attosecond pulse train. The time resolution in these experiments was achieved by measuring the accumulated phase of the free electron wave packet after photoemission using an interferometric technique. The phase carries temporal information about the ionization process, from which the delay in photoemission can be determined with a much better time resolution than that given by the temporal structure of the pulse train. The same technique was applied to investigate the phase behavior of resonant two-photon ionization in helium atoms. The second part describes the application of an interferometric pump-probe technique to characterize bound electron wave packets. Single attosecond pulses are used to excite a broad electron wave packet containing bound and continuum states. The bound part of the wave packet is further ionized by an infrared laser with a variable delay. Analysis of the resulting interferogram allows for full reconstruction of the bound wave packet, since both the amplitude and the phase of all ingoing states in the wave packet are encoded in the interference pattern.
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| 6. |
- Klünder, Kathrin, et al.
(author)
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Probing Single-Photon Ionization on the Attosecond Time Scale
- 2011
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In: Physical Review Letters. - 1079-7114. ; 106:14
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Journal article (peer-reviewed)abstract
- We study photoionization of argon atoms excited by attosecond pulses using an interferometric measurement technique. We measure the difference in time delays between electrons emitted from the 3s(2) and from the 3p(6) shell, at different excitation energies ranging from 32 to 42 eV. The determination of photoemission time delays requires taking into account the measurement process, involving the interaction with a probing infrared field. This contribution can be estimated using a universal formula and is found to account for a substantial fraction of the measured delay.
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| 7. |
- Klünder, Kathrin, et al.
(author)
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Reconstruction of attosecond electron wave packets using quantum state holography
- 2013
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In: Physical Review A (Atomic, Molecular and Optical Physics). - 1050-2947. ; 88:3
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Journal article (peer-reviewed)abstract
- We present a method for performing quantum state holography, with which we completely characterize the amplitude and phase of an attosecond electron wave packet. Our approach is an extension of a recent publication [J. Mauritsson et al., Phys. Rev. Lett. 105, 053001 (2010)] in which we demonstrated experimentally that the energies and amplitudes of an attosecond electron wave packet can be characterized using attosecond electron interferometry. Here we show theoretically that attosecond electron interferometry can be extended to retrieve the phases of all the states that make up the wave packet. We demonstrate the feasibility of our method by analyzing a wave packet created by a shake-up process. We show that our method can successfully retrieve arbitrary phases and/or lifetimes added to the component eigenstates.
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| 8. |
- Mauritsson, Johan, et al.
(author)
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Attosecond electron interferometry
- 2013
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In: Attosecond Physics : Attosecond Measurements and Control of Physical Systems - Attosecond Measurements and Control of Physical Systems. - Berlin, Heidelberg : Springer Berlin Heidelberg. - 1556-1534 .- 0342-4111. - 9783642376221 - 9783642376238 ; 177, s. 121-134
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Book chapter (peer-reviewed)abstract
- Attosecond extreme ultraviolet light pulses have the potential to resolve the ultrafast electron dynamics that govern basic properties of atoms, molecules, and solids. Here we present three different interferometric pump-probe methods aiming to access not only the temporal dynamics, but also state specific phase information after excitation/ionization using attosecond pulses.
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| 9. |
- Mauritsson, Johan, et al.
(author)
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Attosecond Electron Spectroscopy Using a Novel Interferometric Pump-Probe Technique
- 2010
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In: Physical Review Letters. - 1079-7114. ; 105:5
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Journal article (peer-reviewed)abstract
- We present an interferometric pump-probe technique for the characterization of attosecond electron wave packets (WPs) that uses a free WP as a reference to measure a bound WP. We demonstrate our method by exciting helium atoms using an attosecond pulse (AP) with a bandwidth centered near the ionization threshold, thus creating both a bound and a free WP simultaneously. After a variable delay, the bound WP is ionized by a few-cycle infrared laser precisely synchronized to the original AP. By measuring the delay-dependent photoelectron spectrum we obtain an interferogram that contains both quantum beats as well as multipath interference. Analysis of the interferogram allows us to determine the bound WP components with a spectral resolution much better than the inverse of the AP duration.
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| 10. |
- Mikkelsen, Anders, et al.
(author)
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Photoemission electron microscopy using extreme ultraviolet attosecond pulse trains
- 2009
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In: Review of Scientific Instruments. - : AIP Publishing. - 1089-7623 .- 0034-6748. ; 80:12
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Journal article (peer-reviewed)abstract
- We report the first experiments carried out on a new imaging setup, which combines the high spatial resolution of a photoemission electron microscope (PEEM) with the temporal resolution of extreme ultraviolet (XUV) attosecond pulse trains. The very short pulses were provided by high-harmonic generation and used to illuminate lithographic structures and Au nanoparticles, which, in turn, were imaged with a PEEM resolving features below 300 nm. We argue that the spatial resolution is limited by the lack of electron energy filtering in this particular demonstration experiment. Problems with extensive space charge effects, which can occur due to the low probe pulse repetition rate and extremely short duration, are solved by reducing peak intensity while maintaining a sufficient average intensity to allow imaging. Finally, a powerful femtosecond infrared (IR) beam was combined with the XUV beam in a pump-probe setup where delays could be varied from subfemtoseconds to picoseconds. The IR pump beam could induce multiphoton electron emission in resonant features on the surface. The interaction between the electrons emitted by the pump and probe pulses could be observed. (C) 2009 American Institute of Physics. [doi:10.1063/1.3263759]
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